The aeronautical sector faces challenges in meeting its net-zero ambition by 2050. To achieve this target, much effort has been devoted to exploring sustainable aviation fuels (SAF). Accordingly, we evaluated the technical performance of potential SAF production in an integrated first- and second-generation sugarcane biorefinery focusing on Brazil. The CO2 equivalent and the renewability exergy indexes were used to assess environmental performance and impact throughout the supply chain. In addition, exergy efficiency (ηB) and average unitary exergy costs (AUEC) were used as complementary metrics to carry out a multi-criteria approach to determine the overall performance of the biorefinery pathways. The production capacity assumed for this analysis covers 10% of the fuel demand in 2020 at the international Brazilian airports of São Paulo and Rio de Janeiro, leading to a base capacity of 210 kt jet fuel/y. The process design includes sugarcane bagasse and straw as the feedstock of the biochemical processes, including diverse pre-treatment methods to convert lignocellulosic resources to biojet fuel, and lignin upgrade alternatives (cogeneration, fast pyrolysis, and gasification Fischer-Tropsch). The environmental analysis for all scenarios shows a GHG reduction potential due to a decrease of up to 30% in the CO2 equivalent exergy base emissions compared to fossil-based jet fuel.@en

Exergy and environmental analyses have been developed to determine the performance of the electricity generation in the Dutch mix. A comparative assessment of diverse technological routes, including fossil and renewable energy resources consumption, is carried out in terms of the exergy costs and specific CO₂ emissions. Hence, an exergoeconomy methodology is used to properly allocate the renewable and non-renewable exergy costs and specific CO₂ emissions among the various products of the polygeneration energy systems. By using a suitable methodology, the distribution of irreversibility throughout the different steps of the energy conversion processes of the Dutch electricity mix is characterized in the light of the Second Law of Thermodynamics. The results may help to propose performance indicators that support the Dutch government and research institutions. To identify sustainable energy planning strategies and fairly comparing electricity generation and end-use processing stages with other types of energy resources, such as fuels used in transportation, residential and industrial sectors. In brief, the weighted average of the renewable and non-renewable unit exergy costs and the specific CO₂ emissions of the electricity generated in each route of the Dutch mix is calculated and compared to another electricity mix with a higher share of renewable energy resources. The weighted average renewable and non-renewable unit exergy costs of the electricity generated in the Netherlands are calculated as c_R = 0.8375 kJ/kJ_E/W and c_NR = 1.7180 kJ/kJ_E/W, respectively (c_R/c_NR= 0.49). Furthermore, the specific CO₂ emissions in the Dutch electricity generation achieve 373.21 g_CO2/kWh_E/W.

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This paper presents the process design and assessment of a sugarcane-based ethanol production system that combines the usage of both mass and heat integration (pinch analysis) strategies to enhance the process efficiency and renewability performance. Three configurations were analyzed: (i) Base case: traditional ethanol production (1G); (ii) mass-integrated (1G2G); and (iii) mass and heat-integrated system (1G2G-HI). The overall assessment of these systems was based on complementary approaches such as mass and mass-heat integration, energy and exergy analysis, exergy-based greenhouse gas (GHG) emissions, and renewability exergy criteria. The performances of the three cases were assessed through five key performance indicators (KIPs) divided into two groups: one is related to process performance, namely, energy efficiency, exergy efficiency, and average unitary exergy cost (AUEC), and the other one is associated to environmental performance i.e., exergy-based CO₂-equation emissions and renewability exergy index. Results showed a higher exergy efficiency of 50% and the lowest AUEC of all the systems (1.61 kJ/kJ) for 1G2G-HI. Furthermore, the destroyed exergy in 1G2G-HI was lower by 7% and 9% in comparison to the 1G and 1G2G cases, respectively. Regarding the exergy-based GHG emissions and renewability performance (λ_index), the 1G2G-HI case presented the lowest impacts in terms of the CO₂-equivalent emissions (94.10 gCO₂-eq/MJ products), while λ_index was found to be environmentally unfavorable (λ = 0.77). However, λ_index became favorable (λ > 1) when the useful exergy of the byproducts was considered.

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Increasing efforts in developing sustainable and economically viable technologies to produce transportation fuels have been made in the last decades. Particularly, the aviation industry has conceived that biojet fuels are vital to decrease 50% of the greenhouse gas emissions by 2050 and to achieve carbon-neutral growth by 2020. Thus, the goal of this study is to rank self-sufficient biorefineries for biojet fuel production in Brazil bases on an exergy-based performance analysis aiming to identify the processes irreversibilities. The production capacity assumed for this analysis covers 10% of the projected fuel demand by 2020 in São Paulo (Guarulhos) and Rio de Janeiro (Galeão) airports and considers that the biojet fuel produced is suitable for blending with fossil jet up to 50%. In this context, the base capacity analysed was 210 kton jet/year considering sugarcane (SC) and SC straw as feedstocks, largely available in Brazil. Hence, 24 scenarios were compared for lignocellulosic and lignin valorization processes. These technological pathways covers eight pre-treatment processes such as dilute acid (DA), dilute acid + alkaline treatment (DA-A), steam explosion (SE), steam explosion + alkaline treatment (SE-A), organosolv (O), wet oxidation (WO), liquid hot water (LHW) and liquid hot water + alkaline treatment (LHW-A), followed by enzymatic hydrolysis. Furthermore, three thermochemical processes for the direct conversion of bagasse and lignin upgrade to renewable jet fuel or electricity were considered (Fast pyrolysis, Gasification Fischer-Tropsch and Cogeneration). The exergy assessment evidenced that combined pretreatment processes with the alkaline treatment (DA-A, SE-A, LHW-A) have a better global exergetic performance than the lignocellulosic pre-treatments carried out standalone (DA, SE, O, WO, and LHW). In addition, the use of fast-pyrolysis as a technology for the lignin residues presented the higher performance for all the scenarios. It is shown that the CO2 equivalent index and the renewability exergy index are appropriate metrics to determinate the environmental impact/renewability performance of the technological pathways. Lastly, the environmental analysis shows that all scenarios lead to a 30% reduction of specific CO2 equivalent emissions in exergy base in comparison to the petroleum-based jet fuel impacts.

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